[chbot] Hot topic Solder paste.

[Mark Atherton]

Well done, that looks excellent.

Yes, you should be able to get away with surface tension holding lighter 
parts on the bottom of the PCB. One way of holding on larger parts on 
the bottom is to screen on some small epoxy dobs, then place the larger 
parts. This whole mess is then reflowed when the adhesive hardens.

-Mark

On 8/12/2019 3:14 PM, Marshland Engineering wrote:
> I did a test run and I could not see any flux till I use my microscope. The
> joints look good. Much less less flux that hand soldering.
>
> http://www.marshland.co.nz/ftp/Misc/ReflowResults.JPG
>
> I originally made single sided PCBs with my oven and used a suggested heat
> profile. All worked fine. Now I playing with double sided ones. I ran a test
> with 2 thermocouples, one top and one bottom of the board to see the
> difference. The best I could do was a 10 degree differential. As this is quite
> small, I guess I need to do both sides at once, not one then the other. If I
> want to do that, I could use lead free for the first one and then leaded for
> the second at the lower temperature. Still experimenting at the moment.
>
> Not sure if a quicker solder temp rise would increase the difference enough
> after the initial preheat soak period to do one side then the other. Need to
> try some component epoxy to do both at once. I guess capillary will hold
> resistors at the bottom but not ICs, big caps or diodes.
>
> Just found this, 137 deg melting point.
>
> https://www.amazon.com/SRA-Temperature-Solder-Paste-SSLTNC-15G/dp/B005C6H26C
>
> That looks like a solution.
>
> Cheers Wallace
>
>
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